Are Veins and Arteries in the Subarachnoid Space?
Yes, both arteries and veins are present in the subarachnoid space, where they traverse through cerebrospinal fluid before penetrating into brain parenchyma.
Anatomical Location and Structure
The subarachnoid space is the CSF-filled compartment between the arachnoid and pia mater layers of the meninges 1. Major cerebral arteries and veins traverse this space extensively, with the vessels surrounded by CSF and connected by delicate trabecular membranes 1, 2.
Major Vessels in the Subarachnoid Space
The internal carotid arteries enter the subarachnoid space near the level of the ophthalmic artery at the skull base, then give rise to the posterior communicating, anterior cerebral, and middle cerebral arteries within this space 1.
All major cerebral artery trunks—the anterior, middle, and posterior cerebral arteries—course through the subarachnoid space before giving off penetrating branches to brain tissue 3.
Veins also traverse the subarachnoid space, though they are less prominently discussed in the anatomical literature compared to arteries 1, 4.
Clinical Significance
Subarachnoid Hemorrhage
The presence of vessels in the subarachnoid space explains why ruptured cerebral aneurysms cause subarachnoid hemorrhage 1. Blood from ruptured aneurysms fills the CSF-containing subarachnoid space, particularly accumulating in the basal cisterns and posterior fossa where CSF flow is slower 1.
Trabecular Architecture
Delicate pial blood vessels traverse the subarachnoid space, and irregular trabeculae partition this space throughout its length, providing abundant opportunities for tumor cells or blood to accumulate and obstruct CSF flow 1. The trabecular membranes that limit the various cisterns are closely related to the vascular division patterns of the principal brain arteries 2.
Perivascular Spaces vs. Subarachnoid Space
As vessels penetrate from the subarachnoid space into brain parenchyma, they carry with them a perivascular space (Virchow-Robin space) that is anatomically distinct from but connected to the subarachnoid space 5, 4. These perivascular spaces surround small arteries and veins as they enter brain tissue from the subarachnoid space 5.
Important Caveats
The leptomeninges (pia-arachnoid) normally separate the subarachnoid space from perivascular spaces, though pathological conditions like subarachnoid hemorrhage can cause blood to extend into perivascular spaces through leptomeningeal leakage 6.
Recent evidence demonstrates preferential CSF flow patterns along major arteries in the subarachnoid space, with perivascular ensheathment facilitating antegrade tracer passage toward brain tissue 3, 4.
The subarachnoid space around major vessels contains relatively large CSF volumes, creating a continuous network that surrounds and penetrates the brain 4.